Craniofacial neural crest forms from the neural plate and adjacent ectoderm by mechanisms which appear to involve modifications in the extracellular matrix (ECM) produced by, and surrounding crest cells. A histological technique, recently developed by the author, now permits unequivocal identification of neural crest precursors in the head of the mouse embryo. This ability to identify crest precursors makes possible a detailed study of the role of the ECM in neural crest formation. Initially, this would be broken down into: 1) a study of changes in the synthesis, deposition and degradation of glycosaminoglycans (GAG's) and 2) a similar study of collagens and glycoproteins. Changes in GAG's would be followed by either staining with alcian blue, or pulse-chase labeling embryos grown in culture with tritiated precursors. The different GAG's and their distribution would then be identified using specific enzyme digestions. Changes in collagens and glycoproteins would be followed using specific immunohistochemical methods. The role of collagens would be further investigated by exposing cultured embryos to cis-hydroxyproline, an inhibitor of collagen deposition. The combined results of these studies would be unusual in that information on changes in all three major elements of the ECM would be available. This would be used to identify the interactions which almost certainly occur among them. Preliminary results further suggest that swelling of ECM surrounding crest precursors forces their displacement and so initiates crest migration. To demonstrate such a new mechanism in crest migration, chick crest aggregates would be grown in vitro on a substrate precluding cell motility. Migration by displacement would be identified as expansion of the aggregate due to swelling of its extracellular spaces. Results of the work proposed above would then be applied to a study of crest related craniofacial defects. Embryos would be exposed to the teratogens, vitamin A (in excess) and 6-diazo-5-oxo-L norleucine (DON) in culture, and screened for defects related to the role of the ECM in neural crest formation and migration. In summary, these results should provide further insights into the role of the ECM in morphogenesis. As applied to neural crest formation and migration it should further our understanding of crest related craniofacial defects in man.